This invention relates to an artificial knee prosthesis, for implantation by surgery into a knee joint as a partial replacement thereof.
The natural knee joint comprises the bottom part of the femur, constituted by the two condyles, the lower parts of the surfaces of which bear upon the complementary shaped upper surface plateaus of the tibia, through the intermediary of cartilage. Connection through the knee is provided by means of ligaments which also provide joint stability and help to absorb stresses applied to the knee. The femur, cartilage and tibia are are normally subjected to fairly heavy compression loading, being called upon to support substantial parts of the weight of the body.
Movement of the normal knee is a complex movement which includes rocking, gliding and axial rotation. Starting from the full extension position, the movement is also one of axial rotation of the femur about the tibia for about the first 10.degree. of rotation. Then this motion converts to a rocking movement in which the femoral condyles roll posterially on the tibial plateaus. At about 20.degree. of flexion, the type of movement changes again, to the gliding motion in which successive points on the femoral condyles slide forward on the tibial plateaus until full flexion is obtained.
The cartilage located between the femoral condyles and tibial plateaus effectively ensures free, smooth and painless flexion of the knee joint in the normal healthy knee. However, when the cartilage becomes damaged, diseased or inflamed, it ceases to function properly and flexion of the knee becomes difficult and painful. This is effectively what happens in various types of arthritis. To alleviate this condition, it is often necessary to remove the cartilage surgically, in whole or in part, with the result that the knee joint has no component or an inadequate component ensuring its free, smooth flexion.